The present invention relates to a novel vacuum circuit-breaker, to a vacuum valve for use in the circuit-breaker, and furthermore to electrodes which are used therein.
An electrode arrangement in a vacuum circuit-breaker comprises a pair of a stationary or fixed electrode and a movable electrode. Each of the above fixed and movable electrodes comprises four individual elements of an arc electrode, an arc electrode support which supports the arc electrode, a coil electrode material which extends from the arc supporter, and an electrode rod at the end of the coil electrode.
The above arc electrode is directly exposed to arc when breaking a high voltage and a large current. Desirable characteristics required for the arc electrode are fundamental requirements such as a large current breaking capacity, a high voltage resistance, a low contact resistance (i.e., an excellent electrical conductivity), an excellent fusion resistance, a low contact wear, and a low cutting current value. It is difficult, however, to satisfy all of the above requirements, and hence, in general, there has been used a material in which given preference are the characteristics considered to be particularly important for a specific use, and the other characteristics are sacrificed to some extent. As an arc electrode material for large current and high voltage break, Japanese Patent Application Laid-Open Publication No. 96204/1988 teaches a method of dissolving Cu in Cr or a Crxe2x80x94Cu skeleton. Furthermore, a similar manufacturing method has also been disclosed in Japanese Patent Post-Examination Publication No. 21670/1975.
The electrode arrangement in a vacuum valve which is located in a vacuum circuit-breaker also comprises a pair of electrodes constituted by a fixed electrode and a movable electrode. Each of the fixed electrode and the movable electrode comprises an electrical contact and an electrode rod extending therefrom, and a plate of a stainless steel or the like is often provided as a reinforcing plate on the back side of the electrical contact.
Crxe2x80x94Cu composite metals or Crxe2x80x94Cu composite with small additions of other elements such as W, Co, Mo, V and Nb are frequently used as the materials for the electrical contacts for large current and high voltage break.
The above electrical contacts are manufactured by forming the constituent metal powders or mixture thereof into a compact with predetermined composition, shape, and hole volume. The compact thus formed is subsequently sintered to form a skeleton into which Cu or an alloy flux thereof is forced to permeate by a so-called infiltration method. Alternatively, the compact is given high density in the pre-infiltration sintering process by a so-called powder metallurgy method. The electrical contacts obtained in this manner are further machined into the desired shape.
On the other hand, the electrode rod is formed by cutting a pure Cu material into a predetermined shape.
After each of the elements manufactured as described above is assembled, brazing is performed, thereby combining the elements into individual electrode structures. However, electrodes which are constructed through brazing requires excessive time and effort for assembly due to machining and brazing for every element, and furthermore, brazing deficiencies will lead to electrode breakage or fall-off.
As a solution to the above problems, a so-called one-piece infiltration method has been developed, by which the above electrical contact and electrode rod are combined into one unit in the manufacturing stage. More specifically, a highly conductive metal for forming the electrode rod is placed and held on a skeleton which has been formed to the required composition, shape, and hole volume from the mixed powder of components for the electrical contact. The assembly is heated to infiltrate the highly conductive metal into the electrical contact and to form the electrode rod with the remaining highly conductive metal. This method is disclosed in Japanese Patent Application Laid-Open Publication No. 29461/1995.
According to the one-piece infiltration method, pre-brazing assembling operations and brazing operations become unnecessary to remarkably reduce the production stages, and furthermore, electrode breakage or fall-off caused by brazing deficiencies is eliminated, thereby providing electrodes of superior reliability and safety. On the other hand, there occurs consumption of the electrical contact component to a certain degree into the electrode rod side due to dispersion and solidification. The skeleton of the electrical contact therefore has to be formed larger by the consumed volume, thus increasing the manufacture cost. Furthermore, the consumed volume of the electrode varies widely due to non-uniformity in composition and hole volume of the skeleton. Consequently, there occurs an irregularity in position of the interface between the electrical contact and the electrode rod, and the manufacturing yield deteriorates.
Further, large ingot piping occurs in the upper portion of post-infiltration ingots. The electrode has to be cut from the material excepting the ingot piping, and the material is largely wasted.
The electrical contact described above is provided with slit grooves for imparting a driving force to arcs generated, thereby moving the arcs to the periphery of the electrode and preventing the arcs from stagnating. The slit grooves divide the electrical contact into vane-shaped segments. These slit grooves are machined with end mills, etc. after the infiltration process. The machining takes much time because the grooves are in a curved shape.
Moreover, there arise further problems that assembling for joining the manufactured electrical contact to the electrode rod requires time, and that because of the use of brazing flux and the necessity of brazing, associated costs are incurred. In addition, application of heat during the brazing causes vaporization of the brazing flux which subsequently adheres to the contact surface, thereby resulting in instability of the current breaking performance.
An object of the invention is to provide a vacuum circuit-breaker, a vacuum valve used in the circuit-breaker and electrodes for the vacuum valve, which can reduce the manufacturing process while being of high performance and compact in size.
The invention features a vacuum circuit-breaker comprising a vacuum valve which has fixed and movable electrodes in a vacuum container, conductive terminals for connecting the respective fixed and movable electrodes in the vacuum valve to the outside thereof, and switching means for driving the movable electrode, wherein the fixed and movable electrodes each comprise arc electrodes, whose entire surfaces, mutually facing each other, are made of an alloy containing a refractory metal and a highly conductive metal, and electrode rods of a highly conductive metal supporting the respective arc electrodes, and each arc electrode and the mating electrode rod are integrally formed by means of solid-phase diffusion bonding, preferably simultaneously with the formation of the arc electrode through sintering.
Further, the invention resides in a vacuum circuit-breaker which is characterized in that the fixed and movable electrodes each have a plurality of grooves which are formed in their surfaces facing each other from the inner sides thereof to the outsides except central portions of the electrodes. Each groove penetrates completely the arc electrode, and a recess is formed in the central portion of the surface of each electrode.
Furthermore, the invention resides in a vacuum valve having the fixed and movable electrodes described above and also in vacuum-valve electrodes comprising these electrodes.
The invention is directed to the vacuum valve having a pair of fixed and movable electrodes in a vacuum container, preferably a cylindrical insulation container, wherein the fixed and movable electrodes comprise compacts serving as arc electrodes, each of which is made through the pressure formation of a shaped body from an alloy powder of a refractory metal and a highly conductive metal, or a powder mixture of a refractory metal powder and a highly conductive metal powder, and each of which is in a shape having vanes or blades separated preferably by slit grooves and a central recess. Each compact is coupled to the electrode rod of the construction described above, which is formed from a highly conductive metal or alloy and has a protrusion on the central axis thereof, with the protrusion of the electrode rod fitted into the recess of the compact. They are heated to a temperature below the melting point of the highly conductive metal to sinter the compact and simultaneously join the electrode and the electrode rod into a metallurgically-bonded unit by solid-phase diffusion bonding.
A reinforcing plate, which is made of austenitic stainless-steel plate and has a central hole, is provided on the rear side of the arc electrode. The reinforcing plate is positioned between the compact and the electrode rod, and the protrusion of the electrode rod is inserted in the reinforcing plate. The reinforcing plate is fixed to the rear side of the arc electrode by means of diffusion bonding through heating simultaneous with the sintering of the arc electrode.
The refractory metal contained in the above compact is preferably one of the following or is a mixture or compound of two or more of the following: Cr, W, Mo, Ta, Nb, Be, Hf, Ir, Pt, Zr, Ti, Fe, Co, Si, Rh, or Ru. Similarly, the highly conductive metal is preferably Cu, Ag, Au, or an alloy having the main constituent of Cu, Ag, or Au.
It is preferable that the alloy powder of the refractory metal and the highly conductive metal, or the powder mixture of the refractory metal powder and the highly conductive metal powder, contains 15% to 40% by weight of the refractory metal, and 60% to 85% by weight of the highly conductive metal.
Furthermore, it is favorable that the particle size of the alloy powder of the refractory metal and the highly conductive metal, or of the powder mixture of the refractory metal powder and the highly conductive metal powder is 104 xcexcm or less. With regard to the tolerance of fitting of the protrusion on the electrode rod into the recess in the compact, a tolerance in the range of 0.5% to 4% of the recess dimension is desirable when the particle diameter of the alloy powder or powder mixture is between 61 xcexcm and 104 xcexcm inclusive. A tolerance in the range of 1.5% to 9% of the recess dimension is desirable when the particle diameter of the alloy powder or powder mixture is 60 xcexcm or smaller.
It is desirable that the arc electrode and the electrode rod, which are metallurgically bonded into an integrated element by sintering of the above compact, have a pull-apart strength of no less than 200 kgf or more in the direction of insertion. With this strength, it can be ensured that disconnection of the arc electrode at the bonded section can be prevented even when it fuses with the mating electrode.
Each vacuum-valve electrode according to the invention comprises the arc electrode and the above-mentioned electrode rod extending therefrom, in which arc electrode are provided slit grooves of a curved shape for moving arcs generated. The arc electrode is divided into preferably vane or blade-shaped sections by the grooves. The slit grooves can be realized in a quick and simple manner by pressure forming of a charge of the material powder of the arc electrode in a die which is capable of forming a vane-type structure with slit grooves. By sintering the vane-type compact thus formed at a temperature lower than the melting point of the high-conductivity-metal constituent contained therein, it is possible to realize the arc electrode while the vane-type configuration with the above slit grooves remains intact. With this process, the grooves require no machining after the sintering, thereby enabling a remarkable reduction of the processing time. The outer ends of the slit grooves may be kept uncut during the formation and sintering and be cut through outer-edge machining after the sintering, thereby preventing distortion due to sinter shrinkage.
The recess is formed in the center of the above compact by die formation. The recess, when sintering with the protrusion. on the central axis of the arc electrode fitted therein, comes into a so-called shrinkage fit condition due to the shrinkage and solid-phase diffusion bonding of the compact, so that the arc electrode and the electrode rod are metallurgically bonded into one unit in the sintering process. With this process, a brazing stage becomes unnecessary, no use of brazing flux prevents defects in the joint due to the heat of the arc upon current breaking, and furthermore, the current breaking performance can be prevented from deteriorating due to scattering of components of the brazing flux.
Although the arc electrode of the invention is made of the alloy containing the refractory metal and the high conductivity metal, it may have a layer or stratum of only the highly conductive metal on the electrode-rod side to thereby allow the electrical resistance of the arc electrode to be lowered and the material costs to be reduced. Also, the reinforcing plate of austenitic stainless-steel is provided on the rear side of the arc electrode to prevent deformation of, or damage to, the arc electrode as a result of impact during electrode opening and closing. The central hole of the reinforcing plate has the same shape and size as those of the recess in the compact, and can be affixed to the rear of the electrical contact through sintering while being positioned between the compact and the electrode rod and fitted to the protrusion of the electrode rod.
A formation pressure for the above compact is preferably 1.5 ton/cm2 to 4 ton/cm2. If the formation pressure is smaller than this range, the density of the formed compact would be reduced, and the compact would tend to break. On the other hand, if the formation pressure is larger than the above range, the formed compact would have an increased density and be difficult to join to the electrode rod because the shrinkage during sintering is reduced.
By setting the compounding ratio of the refractory metal and the highly conductive metal at 15% to 40% by weight of the refractory metal and 60% to 80% by weight of the highly conductive metal, it is possible to realize a vacuum valve which is excellent in current breaking performance and voltage resistance characteristics while having a relatively low electrical resistance.
Furthermore, by setting the particle size of the material powder containing the refractory metal and the highly conductive metal at 104 xcexcm or less, the surface of the electrical contact has a uniformly fine structure; excellent current breaking performance, voltage resistance, and fusion resistance can be realized; and the shrinkage of the compact increases to enable it to be joined to the electrode rod firmly. If the material powder has a poor flow characteristic and is hardly charged in the die, an appropriate binder may be added to make it in granular form by means of spray drying, etc. In addition, the protrusion on the electrode rod and the recess in the compact can be placed in an appropriate joining condition by setting the tolerance of fitting at a value within the range of 0.5% to 4% of the recess size when the particle diameter of the material powder of the compact is between 61 xcexcm and 104 xcexcm and at another value within the range of 1.5% to 9% when the particle size is 60 xcexcm or smaller. In other words, if the fitting tolerance is smaller than the above range, shrinkage of the compact would be inhibited to thereby make it impossible to obtain a sound sintered element. On the other hand, if the fitting tolerance is larger than the above range, the effectiveness of shrink-fitting on the protrusion of the electrode rod would be diminished, thereby rendering it impossible to obtain sufficient joint strength.
The invention is directed to a vacuum circuit-breaker comprising a vacuum valve with fixed and movable electrodes in a vacuum container, which is preferably an insulation container, conductive terminals connecting the respective fixed and movable electrodes in the vacuum valve to the outside thereof, and switching means for driving the movable electrode preferably through an insulation rod connected thereto. Each of the fixed and movable electrodes comprises an arc electrode made of an alloy containing refractory metal particles, a highly conductive metal and preferably a low-melting-point metal; an electrode support of a highly conductive metal supporting the arc electrode; and an electrode rod of a highly conductive metal having a rear conductor smaller in diameter than the electrode support and an external connection conductor larger in diameter than the rear conductor.
The electrode support and the electrode rod are formed into one unit simultaneously with sintering or by solid-phase diffusion bonding.
For the arc electrodes and the electrode supports, the refractory metal particles are preferably contained at the following percentages by weight with respect to the complete refractory metal: 5% or less for particle sizes of more than 140 xcexcm; 45% to 90% for particle sizes of 70 xcexcm to 140 xcexcm; 7% to 35% for particle sizes of 40 xcexcm to 70 xcexcm; and 0.5% to 15% for particle sizes of less than 40 xcexcm.
The arc electrodes particularly preferably comprise one of or a mixture of Cr, W, Mo and Ta which have melting points of 1800xc2x0 C. or more among the above refractory metals and in which the amount of a dissolved metal is 3% by weight or less based on the weight of Cu, a composite material of the highly conductive metal comprising one of Cu, Ag and Au, or the highly conductive alloy mainly comprising these highly conductive metals. The above electrode support preferably comprises the above highly conductive metal or alloy.
Furthermore, the arc electrodes preferably comprise a composite material of 15 to 40% by weight of the total amount of one or more of Cr, W, Mo and Ta as the refractory metals and 40 to 85% by weight of one of Cu, Ag and Au as the highly conductive metals, or an alloy mainly comprising the highly conductive metals. Moreover, the above electrode support, the rear conductor and the external conductor connection preferably each comprise an alloy of 2.5% by weight or less, preferably 0.5 to 2.5% by weight of the total amount of one or more of Cr, Ag, W, V, Nb, Mo, Ta, Zr, Si, Be, Ti, Co and Fe, and Cu, Ag or Au, so that loading endurance can be remarkably improved. As a result, the thus obtained arc electrode can sufficiently withstand an increase in the contact pressure between the electrodes and an impact force at the time of opening/closing of the electrodes, and it can also inhibit a deformation with time. Particularly, in the case that a rated voltage is 10 kV or less, the content of the refractory metal is preferably in the range of 15 to 40% by weight, and in the case that it is more than 10 kV, the content of the refractory metal is preferably in the range of 40 to 60% by weight.
The arc electrode in the invention comprises the composite alloy of the refractory metal and the highly conductive metal, and the arc electrode and the electrode rod are integrally formed by sintering or solid-phase diffusion bonding at the time of formation of the arc electrode.
The electrode support in the invention preferably has a 0.2% stress of 10 kg/mm2 or more and a relative resistance of 2.8 xcexcxcexa9cm or less.
In a further feature of the invention, the fixed and movable electrodes each have circular recesses formed in the centers of their arc electrodes that mutually contact each other.
The arc electrode and the electrode support are formed by sintering of powder metallurgy, and simultaneously the electrode rod is integrally formed by solid phase diffusion bonding.
The number of the slit grooves described above is plural, preferably in the range of 3 to 6, and they each have a spiral shape. Therefore, the arc electrode preferably has the above vane or blade-like shape divided by the slit grooves. They are formed in the arc electrode or in both the arc electrode and the electrode support. The slit grooves may be straight.
The plurality of slit grooves of the invention described above, each of which extends from the center of the electrode towards the outer periphery and reaches the side of the electrode from the outer-edge side thereof, provide a plurality of arc travel surfaces which are formed between pairs of the slit grooves, and connection sections which each straddle the slit grooves between slit groove outer peripheries and the electrode outer edges to interconnect the individual arc travel surfaces, and which also have the same resistance value as the arc travel surfaces, wherein the path of current flowing in one arc travel surface is set longer than that of another arc travel surface. It is preferable that the cross-sectional areas of the connection sections are adjusted to control the current flowing from adjacent arc travel surfaces into each connection section therebetween.
The invention is further directed to a vacuum circuit-breaker having a vacuum valve with fixed and movable electrodes in a vacuum container, conductive terminals connecting the respective fixed and movable electrodes in the vacuum valve to the outside thereof, and switching means for driving the movable electrode. The fixed and movable electrodes each comprise arc electrodes, each of which is made of an alloy containing refractory metal particles and a highly conductive metal, and electrode supports which support the respective arc electrodes and are made of a highly conductive metal.
The arc electrode and one of the electrode rod and the electrode support are formed into one unit by sintering or by solid-phase diffusion bonding. The insulating container is circular, and the product y of a rated voltage (kV) and an effective breaking current value (kA) lies within the range from a value given by the following equation (1) to a value given by the following equation (2) based on the outer diameter x (mm) of the insulating container:
y=11.25 xxe2x88x92525xe2x80x83xe2x80x83(1)
y=5.35 xxe2x88x92242xe2x80x83xe2x80x83(2).
The invention further features that the diameter y (mm) of the arc electrode lies within the range from a value given by the following equation (3) to a value given by the following equation (4) based on the product x (kVAxc3x97103) of the rated voltage (kV) and the effective breaking current value (kA):
y=0.15 x+22xe2x80x83xe2x80x83(3)
y=0.077 x+20xe2x80x83xe2x80x83(4).
The invention further features that the vacuum container is circular and the diameter y (mm) thereof lies within the range from a value given by the following equation (5) to a value given by the following equation (6) based on the diameter x (mm) of the arc electrode:
y=1.26 x+10xe2x80x83xe2x80x83(5)
y=1.26 x+30xe2x80x83xe2x80x83(6).
A set of three vacuum valves is used with respect to three phases, and it is preferable that the three vacuum valves are arranged laterally and assembled into a single unit through plastic insulation tubes.
The invention is further directed to a vacuum valve having fixed and movable electrodes in a vacuum container which is maintained at a high vacuum. The fixed and movable electrodes each comprise arc electrodes, which are made of an alloy containing refractory metal particles, a highly conductive metal and preferably a low-melting-point metal; electrode supports of a highly conductive metal which support the respective arc electrodes; and electrode rods of highly conductive metal, each having rear conductors smaller in diameter than the arc supports and external connection conductors larger in diameter than the rear conductors. Each electrode support and the associated electrode rod are formed into one unit by sintering or by solid-phase diffusion bonding.
The vacuum-valve electrodes according to the invention are of the same structure as described above.
Although pure Cu is preferable as the material for the arc electrode supports, the strength of the material is low, and therefore, it is preferable that a steel-system material such as pure Fe or stainless steel is used to reinforce the supports to prevent deformation of the electrodes.
Furthermore, it is preferable that a double-strata construction be implemented for the arc electrode and the subsequent elements of the electrode support, etc. The electrode support and the subsequent elements are for reinforcing and supporting the arc electrode, and their thickness is preferably half or more of the thickness of the arc electrode, although it is particularly favorable that the thickness of the former is equal to or more than the thickness of the arc electrode. With regard to the refractory metal, in particular, 0.1% to 10% by weight, or preferably 0.5% to 2% by weight, of one or more of Nb, V, Fe, Ti, and Zr can be added as means for increasing the refractory metal content.
It is preferable that the arc electrode be formed from a Cu alloy which contains in particular 30% to 60% by weight Cr and 0.5% to 5.0% by weight, preferably 0.5% to 3.0% by weight, Nb or alternatively from a Cu alloy containing 0.1% to 0.5% Pb by weight which contains in particular 30% to 60% by weight Cr and 0.5% to 5.0% by weight, preferably 0.5% to 3.0% by weight, Nb.
As described above, because the arc electrode and the subsequent elements of the electrode support, etc. are not mechanically joined but are of a metallurgically continuous, integrated construction, and because the elements are in a high-strength combination, it is possible to provide a vacuum circuit-breaker which is highly reliable and safety without any bad influence as compared with conventional vacuum circuit-breakers.
As described above, it is preferable that the arc electrodes are formed in the blade or vane-shape with the curved slit grooves, which are for moving the arcs generated. The slit grooves can be realized in a quick and simple manner by pressure forming a charge of the material powder of the electrical contact in a die which is capable of forming the vane-type structure. Then, by sintering the vane-shaped compact obtained through the pressure formation at a temperature lower than the melting point of the high-conductivity-metal constituent contained therein, an element can be manufactured with the vane shape having the slit grooves. If the outside ends of the slit grooves are uncut and in the state of being joined, the strength of the electrical contact can be increased. Moreover, in order to prevent distortion due to sinter shrinkage, the outer ends of the slit grooves may be kept in the joined condition during the formation and sintering and be cut by outer edge machining after sintering.
The electric contact may have a layer or stratum of only a highly conductive metal on the electrode-rod side. With this construction, the electrical resistance of the electric contact can be lowered, and associated material costs can be reduced. Additionally, a further stratum may be provided on the electrode-rod side, which is made of an alloy powder containing Cu as the main constituent and one or more of Ni, Ti, Zn, Cr, Cd, and Be. With this additional stratum, the strength of the electrical contact is improved, and damage to the electric contact due to impact during electrode opening and closing can be prevented.
It is desirable that the arc electrode and the arc electrode support and the electrode rod be metallurgically joined into one unit during the sintering process. More specifically, the electrode rod, the arc electrode, and the support therefor, which have been formed in desired shapes, are placed and held with the mating surfaces thereof in the correct orientation, and they are sintered in a vacuum or a reducing atmosphere to be diffusion-bonded. In addition, when the arc electrode support is formed with the recess, the protrusion on the electrode rod is fitted in the recess, and they are joined through shrink-fitting of the protrusion due to sinter shrinkage of the electrical contact, a more rigid joining condition can be achieved.
The reinforcing plate of stainless steel, etc. may be disposed between the arc electrode support and the electrode rod when necessary. Specifically, the reinforcing plate is formed with a hole of the same size as the recess provided in the electrical contact, and the protrusion on the electrode rod is passed through the hole in the reinforcing plate and inserted into the recess in the electrical contact. Upon sintering, the reinforcing plate can be secured in position. Alternatively, if the reinforcing plate has the same main constituent material as that of the electrical contact, diffusion bonding may be employed.
As described above, according to the invention, it is possible to combine the electrical contact and the electrode rod into a single integrated unit through the sintering process without using brazing flux. Further, unlike the one-piece infiltration method, no solid solution or diffusion of electrical contact constituents to the electrode-rod side occurs, and electrical contacts of desired dimensions can be achieved with reliability.
Vacuum circuit-breakers are used along with disconnecting switches, grounding switches, lightning arresters, and current transformers, and are employed in high voltage incoming transfer systems which are indispensable for the supply of power in high-rise buildings, hotels, intelligent buildings, underground shopping centers, oil complexes, all types of manufacturing facilities, railway stations, hospitals, assembly halls, electric trains, substations, and public facilities such as water and sewer service installations, etc.